Cocoa beans are the principal raw material for chocolate production. These seeds are derived from the fruit pods of the tree Theobroma cacao, which is cultivated in plantations in the equatorial zone, e.g., in Ivory Coast, Ghana, and Indonesia. The cocoa beans are embedded in a mucilaginous pulp inside the pods. Raw cocoa beans have an astringent, unpleasant taste and flavour, and have to be fermented, dried, and roasted to obtain the desired characteristic cocoa flavour and taste. The chocolate flavour is influenced by the origin of the cocoa beans, the cocoa cultivar, the on-the-farm fermentation and drying process, and the roasting and further processing performed by the chocolate manufacturer.
After removal of the beans from the pods, the first step in cocoa processing for example for the cocoa variety Forastero is a spontaneous 6 to 10-day fermentation of beans and pulp in heaps, boxes, baskets, or trays. During such process, the beans are freed from adhering pulp. At the end of this period the decomposed pulp is generally washed away by water and the beans dried to produce the cocoa beans of commerce.
A microbial succession of yeasts, lactic acid bacteria (LAB), and acetic acid bacteria (AAB) takes place during fermentation. The yeasts depectinise the pulp and produce ethanol from sugars and citric acid under anaerobic conditions in an acid, carbohydrate-rich environment. As more pulp is drained away, more ethanol is produced and both temperature and pH increase, creating ideal conditions for the growth of LAB and AAB. LAB convert sugars and organic acids into lactic acid. As more air is coming in, AAB start to develop and oxidize the ethanol initially produced by the yeasts to acetic acid. Ethanol and acetic acid diffuse into the beans and this, in combination with the heat produced by this exothermic bioconversion, causes the death of the seed embryo. This in turn initiates biochemical changes in the beans leading to the formation of precursor molecules for the development of a characteristic aroma, flavour, and colour of the beans. These properties are further developed during drying, roasting, and final processing of well-fermented cocoa beans. The activity of yeast, LAB, and AAB is thus essential for the production of high-quality cocoa.
However, the spontaneous cocoa fermentation process is very inhomogeneous and suffers from great variations in both microbial counts and species composition and hence metabolites. The variations seem to depend on many factors including country, farm, pod ripeness, post-harvest pod age and storage, pod diseases, type of cocoa, variations in pulp/bean ratio, the fermentation method, size of the batch, season and weather conditions, the turning frequency or no turning, the fermentation time, etc. which makes reproducibility of fermentation particularly difficult. Because the uncontrolled nature of the usual fermentation process, particularly with respect to the lack of control over the growth and development of microorganisms and metabolic production during the process, the quality of the finished cocoa beans is variable.
Attempts have been made in the prior art to control fermentation parameters.
For instance, WO 2007/031186 discloses a method to regulate the fermentation of plant material consisting of cocoa beans and/or cocoa pulp by adding to said plant material specific bacterial cultures containing at least one lactic acid bacterium and/or at least one acetic acid bacterium at different time points during the fermentation process.
GB 2 059 243 describes a process for the fermentation of cocoa beans with the consecutive use of a pectinolytic yeast and an acetic acid bacterium in an aqueous medium, with agitation and aeration. GB 2 241 146 deals with the mechanical depulping of the cocoa beans before fermentation.
Schwan (1998, Appl Environ Microbiol 64: 1477-83) and Schwan & Wheals (2004, Critical Reviews in Food Science 44: 205-221) disclose the use of starter cultures in cocoa bean fermentation and specifically refer to an inoculum consisting of the strains Saccharomyces cerevisiae var. chevalieri, L. lactis, L. plantarum, Acetobacter aceti and Gluconobacter oxydans subsp. Suboxydans, while Samah et al. (1993, Asean Food Journal, Asean Food Handling Bureau, Kuala Lumpur, MY, vol. 8, no. 1, pg. 22-25) discloses the use of Acetobacter xylinum as inoculum during the fermentation of cocoa beans.
Bhumibhamon et al. (1997a, Kasetsart J. Nat. Science 31:327-341) and Bhumibhamon et al. (1997 b, Kasetsart J. Nat. Science 31:419-428) both refer to the use of specific starter cultures for improving cocoa fermentation. A preferred culture mentioned in Bhumibhamon et al. (1997a) comprises for instance Saccharomyces chevalieri; Saccharomyces cerevisiae and Acetobacter aceti. 
However, fermentation parameters remain difficult to control in prior art methods and industry must therefore address a wide variability in the composition of a batch of processed cocoa beans. Taste problems may occur such as the presence of (too much) acids, a lack of cocoa taste, and too much off-flavour. Therefore, there remains a need in the art for further controlling fermentation processes of cocoa beans in order to obtain cocoa beans having more consistent or improved characteristics, such as highly flavoured cocoa beans of good and reproducible quality. There also remains a need in the art for a reproducible method of fermenting cocoa materials.